End mill having uninterrupted continuously-curved flute surfaces



Feb. 2, 1960 s. M. BABBITT 2,923,053

END MILL HAVING UNINTERRUPTED CONTINUOUSLY-CURVED FLUTE SURFACESOriginal Filed Dec. 10, 1954 20d 20c C. x m

I I 20: 20a

| l g I INVENTOR M M W ATTORNEY United States Patent END MILL HAVINGUNINTERRUPTED CGNTiN- UQUSLY-CURVEDFLUTE SURFACES Seth M. Babbitt,FanWood, N.J., assignor, by mesne assignments, to Eclipse CounterboreCompany, Ferndale, Mich a corporation of Michigan Original applicationDecember .10, 195.4,- Serial No. 474,461, now Patent No. 2,889,669,dated June 9,1959. Divided and this application November 14, 1955,Serial No. 546,477

1 Claim. (Cl. 29-103) This invention relates to fluted toolsand the likeand is concerned more particularly with an improved method and means ofproducing helically fluted workpieces from solid stock solely bygrinding. This-application is a division of my earlier filed applicationSerial No. 474,461, now Patent No. 2,889,669, issued June 9, 19,59.

A primary aim of the invention is to produce complete flutes andaccurately sized cutting edges on a tool such as an end-mill, in a barof previously hardened end-mill stock in a single operation and in aneconomical and eflicient manner. A further object of the invention is todevelop the flutes of an end-mill or similar tool with a continuouslycontoured circumferential surface that runs from the cutting lip ofoneflute into the chip groove and forwardly over the back of a precedingflute lip to the cutting edge thereof, by a grinding operationconductedin a manner such that all rake and clearance angles and cuttingedges associated with each flute are merged into a single sinusoidallycurved surface.

With the aid of this invention helically fluted tools such as end millsmay be produced to size from solid stock, previously hardened. Toolsproduced according to the method herein explained will have allnecessary cutting edges, clearances and chip channels ground thereinin asingle operation and embody. a degree of finish and polish that isunsurpassed in any known prior tool. In accordance with the presentmethod the;bar stock for the end mill is previously'heat treated toobtain the correct hardness and grain andthereafter the shank is groundto size between centers and the portion to be fluted is left a littleoversize. Any distortion incident to heat treating is, therefore,corrected and the bar brought to a size before the cutting edges andflutes are formed. With the present invention theform of the tool, itsnumber of cutting edges and flutes,'the hand and lead of the helix, etc.are ground on the semifinishedsolid cylindrical blank.

Still another aim of the invention is to develop'a method of grindingthat may bepractical at relativelyhigh speeds in producing completeflutesfrom thesolid. 'Heretofore, the conventional practice has been tomill outthe flutes in an untreated blank first With a roughing cut; andthen a finishing cut followed by one or more passes of a cutter toproduce the tooth land and back clearances. After milling, the tool washardened and thereafter several more operations were required forsharpening and correcting inevitable distortion. The present inventionprovides an improved method and means for producing fluted tools,helical or straight,'from the solid previously hardened stock in oneoperation at a highly efiicient rate, leaving only the operation ofsharpening the extreme ends of the cutting lipsto follow to complete thefinished product.

The method, to beexplained in greater detail hereafter, may employ awork-holding spindle mounted for toward and away from the axis of thework. A normal flute grinding operation includes the step of mounting ahardened blank in the chuck of the work spindle, setting the plane ofthe grind-wheel at the angle of the helix to be produced and thenrapidly reciprocating and oscillating the work and causing the rotatingwheel to feed slowly toward the work axis. .On each reciprocatory strokeof the work. spindle the work is moved axially relative to the wheel adistance equivalent to the length of the fluteand simultaneously thework is moved angularly and the rapidly;.rotating grindwheel removes'aportion of the stock. On the return reciprocatory movement of the blankits rotation is reversed and the wheel removes another portion of thestock. During the grinding of a flute the work is caused to reciprocateand oscillate at a rapid rate and with a continuously dressed andfeeding wheela flute'may be completely ground from the solid in a matterof seconds. When the'first flute has been completed the wheel iswithdrawn, the work-spindle is caused to index and the grinding ,of thenext flute proceeds. By this invention a completely finished fluted andsharpenedtool such as an endmill is produced from hardened bar stock. inone set-up including grinding to size and in a matter of moments ascompared with the much longer prior methods of successive milling andsharpening operations.

Other objects and advantages Will be in part indicated in thefollowingdescription and in part rendered apparent therefrominconnection with the annexed drawings.

To cnableothers skilled in the art so fully to apprehend the underlyingfeatures hereof that they may embody the same in the various wayscontemplated by this invention, drawings depicting .a preferred typical.construction have been annexed as a part of this disclosure, and in suchdrawings, like characters of. reference denote corresponding partsthroughout all the views, of which:

Figure 1 of the drawings illustrates diagrammatically a representativeform of grinding apparatus having mounted in a chuck a bar of end millstock that has been previously hardened and its shank end ground betweencenters to. the finished [diameter desired for the end mill.

Figs. 2*5 are views illustrating progressive stages in the grinding of acomplete flute.

.Fig. 6 is anelevation and end view of a completely ground 4-flute endmill.

.Fig. 7 is a diagrammatic view illustrating representative relations ofthe work and wheel.

'Fig. 8 is a diagrammatic sectional View of the zone of engagement ofthe wheel with the work and of the wheel dressing tool with the wheel.

Fig. 9 is a profile view of a wheel dressing cam.

Fig. 10 is a transverse sectional view of work and wheel relationsindeveloping flutes by a combined generating and forming method.

Representative stages of the formation of a single flute in endmill areillustrated inFigs. l-5 in which the nu meral 20 indicates a bar ofend-mill stock that has been previously cut to length, hardened, and itsshank 20a ground between centers, the portion to be fluted may be leftunground if desired. A bar of this character is insertedin a suitablechuck or collet indicated at 21 which isadapted to be oscillated andreciprocated and on 0c-. casions angularly indexed, and on otheroccasions rotated between indexing'movements. The length of thereciprocatory stroke may be varied to suit the flute length and maydesirably be controlled by-cam means indicated at 22 or other form ofmechanism that afiords a high degree of accuracy. The rotary motions inforward and reverse directions may be brought about preferably by ahelically wound band and reciprocable-slide mechanism indicated at23,'tho resort maybe had to other means. In

the mechanism suggested, forward and .reverse angular motion imparted tothe work spindle 21 causes the spindle to travel axially a fixeddistance at a rate determined by the cam means 22 and thefrate of climbof the cam determines the helix angle of the groove 20b to be ground inthe stock 20. The foregoing-mechanisms may be carried preferably in anindexible housing 25, the rotary and indexible movements of which maybecontrolled and actuated by a worm and gear transmission such as 26 andan index plate such as 27.

The grind wheel is indicated at 28 and is angularly adjustable on areciprocable slide 29 that is movable on ways 30 in a directiongenerally radially of the axis of the work 20. The means for effectingrotation of the wheel, its reciprocatory movements between indexing ofthe work spindle, and the means for adjusting the wheel to the helixangle desired, either left or right, may take such form as one maydesire and need not be elaborated upon insofar as the invention of theend mill article and flute forming method here disclosed is concerned.

Suffice it to say that a blank piece of stock 20 is first clamped in thecollet of the work spindle 21, a cam and follower means 22 selected forlength of flute required for the finished end mill, and the spindleoscillating means 23 is angularly adjusted and clamped in accordancewith the rate of climb of the cam. The plane of the grind wheel 28 isthen adjusted and clamped at the proper helix angle of the flutes 20b tobe formed and slightly offset from a true radial line as illustrated inFigs. 7 and 8.

When all adjustments are properly made a work coolant agent is appliedand the work caused to be profusely flushed as the grinding proceeds.For convenience in making the settings above described the wheelcarriage 29 may be caused to occupy a withdrawn position but when thefirst flute forming cycle is initiated the rapidly rotating wheel iscaused to advance toward the work and begin the grinding operation uponthe flooded work. Simultaneously the work is caused to rotate backwardsand forwards and at the same time reciprocate axially at a relativelyrapid rate. The initial contact of the wheel with the work thus causesthe latter to grind a shallow helical line on end mill blank and on eachpass of the work this helical line takes on a curvature and becomesdeeper and deeper until the full length of the flute 20b has beenreached. The method herein disclosed requires on the order of 200 passesof the work per fluteand it is proposed therefore that the wheel becontinuously dressed as the grinding progresses, the dressing being donepreferably in a plane perpendicular to the axis of the work rather thanaxially of the wheel.

After the wheel has reached the required depth in the stock it is causedto be withdrawn and the work indexed one position as, for example, bythe worm gear and index means 26, 27 to present a new portion of thework to the wheel. The cycle is again instituted and the grinding of thesecond flute 20b in the work-piece is caused to occur in the same manneras above explained. A 4-fluted end-mill may be ground from the solid inthis manner with but four indexing movements, a 3-fluted tool with threeindexing movements, and a Z-fluted tool with but two indexing movements.

However, with 2-fluted workpieces, a third movement may be given to thework, namely, a rotary movement between indexes, superposed upon theoscillatory movements. In other words during the oscillatory and reciprocatory movements the work is caused to creep angularly apreselected number of degrees so that during a portion of the flutedevelopment the wheel is generating a cylinder at the core of the tool,the purpose and effect of which is to obtain proper tooth spacing and astrong core or body to back up each cutting edge 200 of the finished endmill. Fig. illustrates diagrammatically the superposed movement and inwhich the zone a is the portion that is generated into a cylinder.

The method herein explained involves, broadly, two cylinderson crossedaxes engaging one another and one of which is given a rotary and axialmotion in reverse directions while the other only revolves and isprogressively fed radially inwardly. Flute contour, by which is meantthe cutting edge 20c of the finished tool, the rake angle 20d and chipgroove 20b leading in a continuous curve and forming land and clearances20c at the cutting edge of a preceding flute, is formed to some extentby the shape developed on the wheel contour and to some extent by thecrossed axes relation of wheel and work. The crossed axes relationcauses theoretical zones of interference that are removed as fast asthey appear by oncoming and leaving portions of the wheel in the regionof engagement, and since the work, with the present method of grinding,is never stationary but continually rotating and moving axially, theresulting flute form is a blend of curves from cutting edge to cuttingedge using a wheel having a simple angular profile that may be easilydressed and maintained in true form. A representative shape of wheelprofile taken in a plane perpendicular to the axis of the work isillustrated in Fig. 8 and an enlarged view of a cam for grinding adiamond dresser to maintain that form is illustrated in Fig. 9. Thissimple wheel profile together with the angular relations and motionsexplained produce the continuous curve on the flute contour. Moreover,the present method of producing an end mill by grinding from the solidhas the further advantage that the grind marks follow the helix of theflute 20b at the cutting edge 20c thereby producing a smooth sharp edgedevoid of the raggedness that is produced by transverse grinding. Forthe same reason the grind marks in the chip groove follow the helix andpromote the expulsion of the chips. These features together with thefact that the forming of the flutes by the present single-operationgrinding method produces a polished surface from cutting edge to cuttingedge and one that is a composition of curves both circumferentially andaxially. Such features impart a degree of strength and freedom and easein action in the present tool that is unsurpassed in tools made by otherprocesses. It will be seen further that the method herein disclosedproduces a finished article, i.e., one that is sharpened and ground tosize in the course of forming the flutes in the bar. The only remainingstep or operation required to complete the tool is that of backing offthe extreme ends of the flutes to provide end cutting lips. Thecontinuous flooding of the work with a coolant during the flute grindingoperation prevents generation of heat and consequent distortion and nocorrective measures need be taken on or to the end mills produced bythis improved method.

Without further analysis, the foregoing will so fully reveal the gist ofthis invention that others can, by applying current knowledge, readilyadapt it for various utilizations by retaining one or more of thefeatures that, from the standpoint of the prior art, fairly constituteessential characteristics of either the generic or specific aspects ofthis invention and, therefore, such adaptations should be, and areintended to be, comprehended within the meaning and range of equivalencyof the following claim.

Having thus revealed this invention, I claim as new and desire to securethe following combinations and elements, or equivalents thereof, byLetters Patent of the United States:

A fluted cutting tool comprising a body portion having 6 ReferencesCited in the file of this patent FOREIGN PATENTS Great Britain July 21,1,702,812 Cochran 1 1929 OTHER REFERENCES 2,129,417 GaSe Sept. 6, 1938 5Wel-don Tools Catalog No. 7-A, June 1936 by the 2,129,413 Gase Sept. 6,1938 Wel-don Tool Co., 321 Frankfort Ave., Cleveland, Ohio.

